Method for producing at least one air product, air separation system, method and device for producing electrical energy

ABSTRACT

A method for producing at least one air product, wherein an air separation system is used which has a primary air compressor, a primary heat exchanger and a distillation column system, and which comprises a first and a second operation mode, wherein, in the first operating mode, at least one liquid air product produced in the distillation column system is saved and, in the second operating mode, the at least one air product saved in the first operating mode and/or at least one additional liquid air product is supplied to the distillation column system.

The invention relates to a method for producing at least one air product, an air separation system, and also a method and a device for producing electrical, energy according to the preambles of the independent claims.

“Condenser-evaporator” designates a heat exchanger in which a first condensing fluid stream comes into indirect heat exchange with a second vaporizing fluid stream. Each condenser-evaporator has a liquefaction chamber and an evaporation chamber which consist of liquefaction passages and evaporation passages, respectively. In the liquefaction chamber, the condensation (liquefaction) of the first fluid stream is carried out, in the evaporation chamber the second fluid stream is vaporized. Evaporation and liquefaction chambers are formed by groups of passages which are in a heat-exchange relationship with one another. The evaporation chamber of a condenser-evaporator can be constructed as a bath evaporator, falling-film evaporator, or forced-flow evaporator.

In the low-pressure column-sump evaporator, in the evaporation chamber, a sump liquid of the low-pressure column is at least in part vaporized. In the low-pressure column intermediate evaporator, in the evaporation chamber, an intermediate liquid of the low-pressure column is at least in part vaporized.

A method of the type mentioned at the outset and a corresponding device having three columns are known from.

In known methods for producing electrical energy, for example the known oxyfuel method, and what are termed combined processes with integrated gasification (integrated gasification combined cycle (IGCC) processes), oxygen or oxygen-enriched gas mixtures are required, for example for combustion or for partial oxidization. To provide the oxygen or corresponding oxygen-enriched gas mixtures, methods and devices for low-temperature separation of air can be used, as are known, e.g. from Hausen/Linde, Tieftemperaturtechnik [low-temperature technology], second edition, 1985, chapter 4 (pages 281 to 337).

In such methods and devices (here called “air separation systems” for short), distillation column systems are used, which can be constructed, for example, as two-column systems, in particular as classical Linde twin column systems, but also as triple- or multicolumn systems. In addition, devices for obtaining further air components, in particular the noble gases krypton, xenon and/or argon, can be provided.

Methods and devices for producing electrical energy should be configured for large load ranges and rapid load changes in order to be able to absorb power fluctuations as can arise owing to the availability or non-availability of other energy feed-ins. Air separation systems which deliver oxygen and/or corresponding gas mixtures therefor should also permit a mode of operation which is flexible to a corresponding extent.

Conventional air separation systems are also affected by the electricity grid utilization and correspondingly highly varying electricity prices.

The degree of flexibilization possible is dependent in this case on the liquefaction capacity of the air separation system. The larger the available liquefaction capacity is, the more favorably power can be stored in the form of liquid air products. In particular, air separation systems for supplying methods and devices for energy production have only a low liquefaction capacity, since they are designed for production of large amounts of gaseous oxygen and nitrogen products that are withdrawn from the air separation system at ambient temperature. The cold requirement of corresponding systems is relatively low, and so they are also not designed to deliver a sufficient amount of cold for the exclusive provision of relatively large amounts of liquid air products.

In corresponding systems, a separate liquefaction system (LIN, LOX or LAIR liquefier) can therefore be installed and connected in during the liquefaction phase. A flexibilization can also be achieved in that the cold production capacity (and therefore correspondingly the liquefaction capacity) of the method or of the system can be designed to be higher than for the actually required amount of gaseous oxygen and nitrogen products.

If relatively large amounts of liquid air products are fed into a corresponding air separation system, possibly significantly more cold can be entered into the air separation system than required. This, without countermeasures, would lead to the respective temperature profiles in the heat exchangers being shifted and the temperature of one or more of the streams exiting from the heat exchangers would become lower and lower. From a certain limit, a reliable mode of operation of the air separation system would no longer be ensured. This problem can be addressed by using heat-producing devices, e.g. air-, steam-, gas-heated or electrically heated heat exchangers, or heat exchangers heated in other ways. Such a solution, however, proves unfavorable, in particular for energetic reasons.

It is an object of the present invention to specify a method of the type mentioned at the outset and corresponding devices that have a large range of variation in the energy consumption thereof and have a comparatively low energy consumption in all corresponding modes of operation.

DISCLOSURE OF THE INVENTION

This object is achieved by a method for producing at least one air product, an air separating system and also a method and a device for producing electrical energy having the features of the independent claims. Preferred embodiments are in each case subject matter of the dependent claims and also of the description hereinafter.

Before the advantages achievable in the context of the present invention are explained, some of the expressions used in this application will be explained.

An “air separation system” is charged with optionally dried and purified air that is provided by means of a “main air compressor” in the form of at least one pressurised air stream. An air separation system has, as mentioned, a distillation column system for separating the air into the physical components thereof, in particular into nitrogen and oxygen. For this purpose, the air is cooled to close to the dew point thereof, and introduced into the distillation column system, as explained above. In contrast thereto, a pure “air liquefaction system” or “liquefaction device” does not comprise a distillation column system. Furthermore, the structure of an air liquefaction system can correspond to that of an air separation system with the delivery of an air liquefaction product. Of course, liquid air can also be produced as a byproduct in an air separation system.

A “liquid air product” is any product which can be produced at least by compression, cooling and subsequent expansion of air in the form of a low-temperature liquid. In particular, it can be in this case, as mentioned, liquid oxygen (LOX), liquid nitrogen (LIN), liquid argon (LAR) or liquid air (LAIR). The expressions “liquid oxygen” or “liquid nitrogen” designate respectively here also low-temperature liquids which have oxygen and/or nitrogen in an amount which is greater than that of atmospheric air. They therefore need not necessarily be pure liquids having nigh contents of oxygen and/or nitrogen. Liquid nitrogen, therefore, is taken to mean not only pure or substantially pure nitrogen, but also a mixture of liquefied atmospheric gases, the nitrogen content of which is higher than that of atmospheric air. For example, it has a nitrogen content of at least 90, preferably at least 99, mol %.

A “low temperature” liquid, or a corresponding fluid, liquid air product, stream etc. is taken to mean a liquid medium, the boiling point thereof being markedly below the respective ambient temperature and being, for example, 200 K or below, in particular 220 K or below.

Examples of low-temperature media in the above sense are liquid air, liquid oxygen and liquid nitrogen.

A “heat exchanger” serves for the indirect transfer of heat between at least two streams conducted in counter flow to one another, for example a warm pressurized air stream and one or more cold streams or a low-temperature liquid air product and one or more warm streams. A heat exchanger can be formed from a single heat-exchanger section or from a plurality of parallel- and/or series-connected heat-exchanger sections, e.g. of one or more plate heat exchanger blocks. A heat exchanger, for example also the “main heat exchanger” used in an air separation system, that is distinguished in that the main fraction of the streams that are to be cooled or warmed are cooled or warmed thereby, has “passages”, which are constructed as fluid channels separated from one another and having heat-exchange surfaces. A corresponding heat exchanger, in operation, has a “warm side” and a “cold side”, the temperatures of which differ. A “warm-side” temperature of a heat exchanger is the temperature at which the streams that are to be cooled are fed to the heat exchanger. Since, optionally, a plurality of streams that are to be cooled are fed to the heat exchanger at differing temperature levels, the warm-side temperature can also relate to the mean or the lowest or highest temperature of the streams that are to be cooled that are fed.

A “compressor” is a device which is equipped for compressing at least one gaseous stream from at least one starting pressure, at which it is fed to the compressor, to at least one final pressure, at which it is taken off from the compressor system. A compressor forms here a structural unit which, however, can have a plurality of “compressor stages” in the form of known piston, screw and/or paddle wheel and/or turbine arrangements (that is to say axial or radial compressor stages). This also applies to a “main air compressor” of an air separation system that is distinguished in that all or the predominant fraction of the amount of air that is fed into the air separation system is compressed thereby. In particular, these compressor stages are driven by means of a shared drive, for example via a shared shaft. A plurality of compressors, e.g. a main compressor and a booster of an air separation system, can be coupled to one another. A “booster” is constructed for further pressure elevation of an already pressurized stream. A “cold compressor” is distinguished in that a corresponding stream can be fed thereto at a low temperature, in particular also in the low-temperature state. The cold compressor in this case is equipped in accordance with the prior art.

An “expansion turbine”, which can be coupled via a shared shaft to farther expansion turbines or energy converters such as oil brakes, generators or compressors, is equipped for expanding a gaseous or at least in part liquid stream. In particular, expansion turbines can be constructed for use in the present invention as turbo expanders. If a compressor is driven by one or more expansion turbines, and, however, is operated without external energy, for example supplied by means of an electric motor, here the expression “turbine-driven” compressor is used. Arrangements of turbine-driven compressors and expansion turbines are also termed “booster turbines”. A “pressurized nitrogen turbine” or “PGAN turbine”, in the context of this application, is termed an expansion turbine by means of which a nitrogen-rich pressurized stream that is produced in the air separation system and is withdrawn from a distillation column system is expanded. The expanded pressurized stream can then be warmed, for example, in the main heat exchanger and blown off to the surroundings. An expansion turbine designated as a “medium-pressure turbine” is used specifically in connection with three-column systems which comprise a high-pressure column, a medium-pressure column and a low-pressure column. A medium-pressure turbine expands a pressurized air stream that is compressed by a main air compressor and optionally boosted in a booster, after cooling in the main heat exchanger into the medium-pressure column. Via an “injection turbine”, in contrast, a pressurized air stream that is compressed by a main air compressor and optionally boosted in a booster, after cooling in the main heat exchanger, is expanded into the low-pressure column of the three-column of a two-column system. A stream that is expanded into the high-pressure column by means of an expansion, valve, in contrast, is termed a “throttled stream”. This stream is compressed in advance to a pressure level above the operating pressure of the high-pressure column, for example by means of a booster in or downstream of the main air compressor and/or by means of a turbine-driven compressor.

A “tank system”, in the context of the present application, is taken to mean an arrangement having at least one low-temperature storage tank equipped for storage of a liquid air product. A corresponding tank system has insulation means.

The present application, to characterize pressures and temperatures, uses the expressions “pressure level” and “temperature level”, which is to express the fact that the corresponding pressures and temperatures need not be used in the form of exact pressure or temperature values, in order to realize the inventive concept. However, such pressures and temperatures typically occur in defined ranges which are, for example, +/−1%, 5%, 10%, 20%, or even 50%, about a mean value.

Corresponding pressure levels and temperature levels can ire in disjoint ranges or in ranges which overlap one another. In particular, for example pressure levels include unavoidable or expected pressure drops, for example on account or cooling effects. The same applies correspondingly to temperature levels. The pressure levels stated here in bar are absolute pressures.

Liquid air products or corresponding liquid streams can be converted by warming into a gaseous or supercritical state. A regular phase transfer by evaporation, proceeds when the warming proceeds at subcritical pressure. If liquid air products, however, are warmed at a pressure which is situated above the critical pressure, on warming above the critical temperature, no phase transfer proceeds in the actual sense, but a transfer from the liquid state to the supercritical state. If, in the context of this application, the expression “evaporation” is used, this also includes the transfer from the liquid state to the supercritical state.

Advantages of the Invention

The invention, proceeds from a method for producing at least one air product in which an air separation system is used that has a main air compressor, a main heat exchanger and a distillation column system. The method comprises in this case, as already addressed at the outset, a first and a second operating mode, wherein, in the first operating mode, at least one liquid air product produced in the distillation column system is stored, and in the second operating mode, the at least one liquid air product (e.g. liquid air, liquid nitrogen or liquid oxygen) that is stored in the first operating mode and/or at least one further liquid air product (e.g. liquid air, liquid nitrogen or liquid oxygen) that is in any case not produced in the second operating mode, and/or an externally fed liquid air product and/or a liquid air product that is temporarily stored in other ways as fed into the distillation column system.

According to the invention it is provided that, in the second operating mode, at least one gaseous pressurized stream at a temperature level that is below a warm-side temperature of the main heat exchanger is fed to a cold compressor, is compressed in the cold compressor from a first superatmospheric pressure level to a second superatmospheric pressure level, and at the second superatmospheric pressure level is fed into at least one distillation column of the distillation column system. This distillation column is operated at an operating pressure which corresponds to the second superatmospheric pressure level. This method offers considerable advantages compared with the prior art.

As already mentioned hereinbefore, feeding in a comparatively small amount of low-temperature liquids or liquid air products into the cold box of an air separation system is frequently readily possible, since, on account of the unavoidable heat incursion owing to the insulation and losses in the (main) heat exchanger (warm-side temperature difference), a certain amount of cold is always required. This amount of cold is generally supplied by an expansion turbine used.

If the cold requirement is covered by the previously described feed-in, the expansion machine can be switched off. This permits a corresponding saving of drive power at the main air compressor and/or a booster connected downstream thereof, if what is termed a medium-pressure turbine is used, in which additionally compressed air is expanded. The same applies similarly, if the corresponding method is realized on the basis of what is termed an injection turbine, by means of which air is expanded to the low-pressure column of the distillation column system used. If what is termed a pressurized nitrogen or PGAN turbine is used, as is shown in the figures presented in the context of this application, switching off the turbine leads to the fact that a large utilisable amount of pressurized nitrogen is available, from which the energy employed for compression can be recovered. For this purpose, an external expansion engine can be used, to which the corresponding pressurized stream is fed after it is heated in an upstream heater, and expands the pressurized stream to the pressure required for the specific field of use (e.g. for use as regeneration gas).

If, with the feed-in of the low-temperature liquids or the liquid air products, however, over a relatively long time, more e old is introduced into the cold box than is required, this can lead to the fact that the temperature profiles in the heat exchangers used change in an unfavorable manner (“shift”), as a result of which the temperature of one or more streams exiting from the heat exchanger becomes lower and lower. From a certain limit, a reliable or as-specified mode of operation of the air separation system is no longer ensured. A further feed-in is then no longer possible, unless the heat incursion into the cold box is increased by an additional heat source. For this purpose, as mentioned, any known heat-producing device can be used, e.g. an air-heated, steam-heated, gas-heated heat exchanger, or a heat exchanger which is electrically heated or heated in some outer way.

In this connection, however, the use of cold compressors (that is to say, as described above, compressors having an intake temperature lower than ambient temperature) has proved to be particularly advantageous, since thereby not only can heat be introduced into the system, but the overall method can be influenced and improved by targeted compression of certain material streams. A corresponding method is illustrated in the FIGS. 1 and 2 that are explained hereinafter. Here (in a “second” operating mode, which is carried out with the feed-in of corresponding low-temperature liquids or liquid air products), the amount of pressurized nitrogen available after shutting off a corresponding expansion turbine (e.g. a pressurized nitrogen turbine, as shown in said figures, but also, for example, an injection turbine) is compressed in the cold compressor, then warmed in a preheater and expanded in a separate expansion turbine. The use of an external expansion turbine with upstream preheater, however, is not satisfactory in all cases, since such hardware components are extremely expensive, and need to be operated with a considerable energy consumption. Thus, for example, typically a separate (medium-pressure) steam system is provided to operate a corresponding preheater. The losses associated herewith are high. A method and/or a system without such apparatus is therefore particularly desirable and advantageous in the sense of reduction of costs and energy savings.

The use of cold compressors in air separation systems is known per se. For instance, in U.S. Pat. No. 7,272,954 B2, a cold compressor is used for compressing a throttled stream. However, this use is diametrically opposed to the aims of the method and of a corresponding system described here: a throttled stream is, as explained, compressed precisely to be able to perform subsequently a corresponding expansion into the high-press tire column for the production of additional cold. The throttled stream is here therefore: compressed to a higher superatmospheric pressure level, but not fed at this pressure into the high-pressure column, but in advance again expanded. In the context of the present invention, in addition, the first superatmospheric pressure level is below the operating pressure of the high-pressure column.

In the already repeatedly mentioned “first operating mode” of a corresponding air separation system, air products that are not necessarily gaseous are provided, for example to an oxyfuel or IGCC method. The first operating mode can also comprise withdrawing liquid air products from a corresponding system and transferring them into storage tanks provided for this purpose (during the mentioned cheap electricity or electricity surplus times). The first operating mode is distinguished, primarily, in that additional cold is generated in the air separation system, for example by means of a pressurized nitrogen turbine, an injection turbine and/or a medium-pressure turbine. In the first operating mode, at any rate, small amounts of air products previously stored in a tank system are fed into the distillation column system used and, as required, further separated, in such a manner that the adverse effects mentioned of an excessive introduction of cold are not established.

In contrast, in the “second operating mode” mentioned, generally no additional cold is generated by means of a pressurized nitrogen turbine, an injection turbine and/or a medium-pressure turbine, because air products stored therein in storage tanks in advance are fed into the distillation column system used, and, as required, farther separated. These air products can also, by means of additional devices or systems, be stored into the storage tanks or provided, for example by means of a separate liquefier. In the second operating mode, the cold compressor is used in order to ensure a heat introduction and at the same time to perform a compression of a corresponding pressurized stream.

The invention thereby provides an air separation system that, using inexpensive means, permits a particularly advantageous operation even in the case of feed-in of relatively large amounts of liquid air products, for example stored in advance in storage tanks. Compared with air separation systems having heated heat exchangers but also in comparison with systems having cold compressors and external expansion turbines, the costs may be significantly reduced.

Of course, the above-explained first operating mode can also be comprised by the method in which the at least one and/or at least one further gaseous pressurised stream is cold-producingly expanded in an expansion turbine. The method can, if required, here be switched over between the two operating modes.

The method can advantageously be used when a distillation column system is used that comprises a high-pressure column and a low-pressure column, wherein the high-pressure column is operated at a higher operating pressure than the low-pressure column. Soon distillation column systems (for example twin-column systems or systems having separate high-pressure and low-pressure columns) are known in principle in the specialist world. The method is therefore suitable for retrofitting a multiplicity of existing air separation systems with corresponding distillation column systems.

In such distillation column systems, the first pressure level corresponds to the operating pressure of the low-pressure column and/or the second pressure level corresponds to she operating pressure of the high-pressure column. The invention permits here a corresponding pressure elevation and transfer into the distillation column system with simultaneously metered cold introduction.

Particular advantages and a still more flexible method procedure result when a distillation column system is used which additionally comprises a medium-pressure column that is operated at an operating pressure which is between the operating pressures of the high-pressure column and the low-pressure column.

Correspondingly, here, the first pressure level can correspond to the operating pressure of the low-pressure column, and the second pressure level can correspond to the operating pressure of the medium-pressure column, or the high-pressure column. Alternatively, the first pressure level can correspond to the operating pressure of the medium-pressure column, and the second pressure level can correspond to the operating pressure of the high-pressure column.

In all cases, the at least one gaseous pressurised stream can be formed from at least a part of a stream that is withdrawn from a distillation column of the distillation column system, which distillation column is operated at the first pressure level as operating pressure, that is to say a low-pressure column or, if present, optionally also a medium-pressure column. After the compression in the cold compressor, the at least one gaseous pressurised stream can be fed at least in part into a distillation column at a higher pressure level (in the event, of withdrawal from the low-pressure column, therefore, the medium-pressure column or the high-pressure column, in the event of withdrawal from a medium-pressure column, she high-pressure column).

As an alternative thereto, the at least one gaseous pressurized stream, however, can also be formed from at least a part of a stream that is provided by means of the main air compressor and is cooled by means of the main heat exchanger, that is to say, for example, from a “medium-pressure stream”, which in part is intended for feed-in into a medium-pressure column of the distillation column system and is at a corresponding pressure. Such a gaseous pressurized stream subsequently compressed in the cold compressor can then be fed into the distillation column that is operated at a corresponding pressure level.

Before it is fed into the respective distillation column, the at least one gaseous pressurized stream can also be combined with at least one further stream at the second pressure level. If such a second pressure level corresponds, for example, to the operating pressure of the high-pressure column, a correspondingly compressed gaseous pressurized stream is therefore combined with a corresponding pressurized air stream, that is provided by a main air compressor at this second pressure level and is cooled in the main heat exchanger.

If the compressed gaseous pressurized stream is not yet air a preset temperature, the at least one gaseous pressurised stream, after the compression in the cold compressor, can be cooled at least in part in the main heat exchanger. This is also an advantageous measure, in order to, by feeding in liquid air products, counteract adverse changes in temperature profiles of the main heat exchanger by targeted temperature entry.

In this case, according to requirements, and as shown, e.g., in FIGS. 9 and 10, a feed-in into the heat exchanger car; take place at any desired point, depending on where a particularly favorable cooling and/or influencing of the temperature profiles can be effected. Thus, the at least one gaseous pressurized stream, after a compression in the cold compressor, can be fed for cooling to the main heat exchanger on the warm side or at a further temperature level, which is below a warm-side temperature of the main heat exchanger.

The method also offers advantages when a part of the gaseous pressurized stream, compressed in the cold compressor is warmed in the main heat exchanger and/or is discharged at least in part from the air separation system. A corresponding stream can be used, for example, as regeneration gas in a purification device with adsorber containers and is available therefor at a particularly favorable pressure and temperature level.

With regard to the features and advantages of the air separation system according to the invention, reference may likewise be made to the advantages explained. Such an air separation system has a main air compressor, a main heat exchanger and a distillation column system and is equipped for operation in the explained first operating mode and the explained second operating mode, wherein means are provided which are equipped for, in the first, operating mode, storing at least one liquid air product produced, in the distillation column system and, in the second operating mode, feeding the at least one liquid air product that is stored in the first operating mode and/or at least one further liquid air product into the distillation column system. Corresponding means can comprise, for example, manual or automated process control switching means. The air separation system has a cold compressor, in addition, means are provided which are equipped to feed, in a second operating mode, the as least one gaseous pressurized stream that is at a temperature level that is below a warm-side temperature of the main heat exchanger to the cold compressor, to compress it in the cold compressor from a first superatmospheric pressure level to a second superatmospheric pressure level, and then to feed it at the second pressure level at least in part into at least one distillation column of the distillation column system.

Also, with regard to the features and advantages of the method according to the invention and the device according to the invention for producing electrical energy, reference may be made to the above explanations, in particular, it can in this case be an oxyfuel or IGCC method, and/or a corresponding device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail with reference to the accompanying drawings. In the drawings:

FIG. 1 shows an air separation system not according to the invention in a first operating mode in the form of a schematic system diagram,

FIG. 2 snows the air separation system according to FIG. 1 in a second operating mode in the form of a schematic system diagram,

FIG. 3 shows an air separation system according to an embodiment of the invention in the second operating mode in the form of a schematic system diagram,

FIG. 4 shows an air separation system according to an embodiment of the invention in the second operating mode in the form of a schematic system diagram,

FIG. 5 shows an air separation system according to an embodiment of the invention in the second operating mode in the form of a schematic system diagram,

FIG. 6 shows an air separation system according to an embodiment of the invention in the second operating mode in the form of a schematic system diagram,

FIG. 7 shows an air separation system according to an embodiment of the invention in the second operating mode in the form of a schematic system diagram,

FIG. 8 shows an air separation system according to an embodiment of the invention in the second operating mode in the form of a schematic system diagram,

FIG. 9 shows a possibility for arranging a cold compressor in an air separation system according to an embodiment of the invention in the second operating mode in the form of a schematic subdiagram, and

FIG. 10 shows a possibility for arranging a cold compressor in an air separation system according to an embodiment of the invention in the second operating mode in the form of a schematic subdiagram.

EMBODIMENTS OF THE INVENTION

Comparable elements bear identical reference signs in the figures and, for the sake of clarity, explanations are not repeated.

In FIGS. 1 to 10, sometimes identical systems and components of such systems are shown in differing operating modes, which differ inter alia in the position of a multiplicity of valves in corresponding lines, in such a manner that liquid and gaseous streams are conducted through different system components. The valves in this case are not shown. Lines that are shut off, however, are shown crossed through (-x-).

FIG. 1 shows an air separation system 110 not according to the invention in the form of a schematic system diagram. The air separation system 110 is shown in FIG. 1 in a first operating mode, in which no significant amounts are fed thereto of liquid air products from “external sources”, e.g. from a storage tank or an air liquefaction system. The first operating mode shown is, for example, for producing liquid air products in cheap power or power excess periods, wherein said liquid air products are stored in corresponding storage tanks and provided for the second operating mode shown with respect to FIG. 2 for feeding into the air separation system 110. A further operating mode can also comprise the exclusive or predominant provision of gaseous air products.

The air separation system 110 comprises, as central components, a main air compressor 10 that is shown highly schematically, a main heat exchanger 20 and a distillation column system 30 that, in the example shown, is constructed as a multicolumn system having a high-pressure column 31, a medium-pressure column 32 and a low-pressure column, wherein the low-pressure column has a first section 38 and a second section 33. These two sections are connected via a gas line k that has no pressure-changing measures and form thereby a unitary distillation space which, with respect, to the separation action, the pressure and the temperatures, cannot be differentiated from a one-piece low-pressure column.

The operating pressure of the high-pressure column 31 is, for example, 5.0 to 5.5 bar at the top, the operating pressure of the low-pressure column 33 is, for example, 1.3 to 1.4 bar at the top. The operating pressure of the medium-pressure column 32 is between the operating pressure of the high-pressure column 31 and the operating pressure of the low-pressure column 33.

To supply the distillation column system 30 and/or the respective columns with corresponding pressurized air, the main air compressor 10 is equipped to provide at least a first pressurized air stream a and a second, pressurized air stream l. The pressure level of the first pressurized air stream a in this case is at the operating pressure of the high-pressure column 31 (therefore also called “high pressure air”, HPAIR), the pressure level of the second pressurized air stream l, in contrast, is at the operating pressure of the medium-pressure column 32 (therefore also termed “medium-pressure air”, MPAIR).

The provision of corresponding pressurized air streams a and l is known in principle and is not explained here in detail. For example, in a main air compressor 10, atmospheric air is taken in by suction via a filter and compressed in multiple stages to said pressures. The first pressurized air scream a can be withdrawn, for example, at the end of a multistage compression, the second pressurized air stream l can be withdrawn at an intermediate site. The air can, after the compression, be cooled with cooling water in direct heat, exchange in a direct contact cooler. The cooling water can be fed from an evaporative cooler and/or from an external source. The compressed and cooled air can then be purified in a purification device. The purification device can have a pair of containers that are filled with a suitable adsorbent. For regeneration of the purification device, a nitrogen-rich regeneration gas, here in the form of the stream v that is described hereinafter, is used.

In the example shown, the first pressurised air stream a at said pressure level is conducted through a passage 21 of the main heat exchanger 20 and there cooled to near the dew point. The cooled pressurized air stream further denoted by a is, downstream of the main heat exchanger 20, in part fed into the high-pressure column 31, and in a further part liquefied in a bath evaporator or bath condenser 34 which is filled with an oxygen-rich liquid (see hereinafter). Of the liquefied fraction, again one fraction is fed into the medium-pressure column 32 in the liquid state and a further fraction is conducted through a subcooler 35 and expanded into the low-pressure column 33.

The second pressurized air stream l is conducted in one part through a passage 24 of the main heat exchanger 20 and there cooled to near dew point. A further fraction, in contrast, is conducted through a heat-exchanger element 44 which can also be integrated in the main heat exchanger 2 0 and there used for vaporizing an oxygen-rich liquid stream n (see hereinafter). The fractions united again subsequently are fed into the medium-pressure column 32.

From the sump of the high-pressure column 31 and the medium-pressure column 32, in each case oxygen-enriched liquid streams are taken off, conducted as stream h through the subcooler 35 and expanded into the low-pressure column 33.

From the sump of the low-pressure column, an oxygen-rich liquid stream i is taken off, boosted by means of a pump 36, transferred via an expansion valve (without a label) into a low-pressure column intermediate evaporator 37, there in part vaporized against a nitrogen-rich stream r (see hereinafter) and transferred into the first section 38 of the low-pressure column, in the sump of which is arranged a low-pressure column bottom evaporator 39. In the example, the two condenser evaporators, the low-pressure column intermediate evaporator 37 and the low-pressure column bottom evaporator 39, are constructed as failing-film evaporators. Liquid and gaseous fractions obtained from the top of the oxygen column 38 are recirculated as stream k in part into the low-pressure column 33. Another part of the liquid flowing out of the evaporation space of the low-pressure column intermediate evaporator 37 is applied as reflux liquid to the first section 33 of the low-pressure column.

From the sump of the low-pressure column 38, a liquid oxygen-rich stream is taken off and transferred to the side condenser 34 which is constructed as a condenser-evaporator with liquid bath (bath evaporator). From the top of the side condenser 34, a gaseous oxygen-rich stream m is taken off, warmed in the main heat exchanger 20 and used for providing a gaseous oxygen pressurized product (here designated GOX). From the sump of the side condenser 34, a liquid oxygen-rich stream is taken off, from which a substream n is boosted in the liquid state, vaporised in the heat-exchanger element 44 and likewise used for providing the gaseous oxygen pressurized product. A substream o, in contrast, is in part subcooled in the subcooler 35 and used for providing a liquid oxygen-rich air product (here designated LOX). The liquid air product can be transferred to a suitable storage tank 61 and stored therein.

From the top of the high-pressure column 31, a nitrogen-rich gaseous stream p is taken off and liquefied in the falling-film evaporator or falling-film condenser 39. A substream is recirculated to the high-pressure column 31, a further substream (cf. link A) is conducted through the subcooler 35 and then expanded into the low-pressure column 33.

From the top of the medium-pressure column 32, a nitrogen-rich gaseous stream r is taken off and in part liquefied, in the falling-film evaporator or falling-film condenser 37. A substream is recirculated to the medium-pressure column 32, a further substream s is conducted through the subcooler 35 and then in part expanded into the low-pressure column 33 and in part provided in the form of a liquid nitrogen-rich air product (here designated LIN). This also can be stored in a suitable storage tank 62.

A further (larger) substream t of the stream r is, in the first operating mode shown, bypassing a cold compressor 45, warmed in the main heat exchanger 20. Again a fraction thereof, here illustrated as stream u, can be withdrawn from the main heat exchanger 20 at an intermediate temperature and then cold-producingly expanded in a “cold” expansion turbine 46 (termed pressurized nitrogen turbine), which can be coupled, for example, to a generator. The fraction which is not expanded in the expansion turbine 45 is provided in the form of a gaseous nitrogen-rich air product (here designated MPGAN). After the expansion in the expansion turbine 45, the stream u is again conducted through the main heat exchanger 20 from the cold end to the warm end and divided on the warm side of the main heat exchanger 20 into the substreams v and w. The substream v is used as regeneration gas (REGGAS) in the main air compressor 10 and/or a purification device assigned thereto (see above). The substream w, in contrast, is warmed by means of a heat exchanger 51 operated by a warm water stream and then expanded in a further expansion turbine 52, which can likewise be coupled to a generator.

From the top of the low-pressure column 33, a nitrogen-rich stream y is taken off, warmed in the main heat exchanger 20 and passed out of the air separation system 110.

As already explained, the use of the expansion turbine 46 serves to deliver an amount of cold that is always required on account of an unavoidable heat introduction via the insulation and via losses in the main heat exchanger (warm-side temperature difference). If this cold, as is shown in the second operating mode of the air separation system 110 which is shown in FIG. 2, is already covered by liquid air products that are fed in, the expansion turbine 46 can be shut off. In the example shown, this leads to a large utilizable amount of a corresponding nitrogen-rich air product being available under pressure, from which energy can be recovered. In other configurations in which, for example, a pressurized stream that is “directly” provided by the main air compressor and cooled in the main heat exchanger is expanded in a corresponding expansion turbine (similar to the expansion turbine 46), in contrast, a decrease in the drive power in the main air compressor 10 can proceed.

In FIG. 2, a corresponding second operating mode of the air separation system 110 is shown. Therein, firstly an oxygen-rich liquid air product (LOX) is transferred (cf. link B) from the storage tank 61 to the bath evaporator or bath condenser 34, and secondly a liquid air product (for example liquefied air from an external liquefier, here designated LAIR), is fed from a further storage tank 63 into the low-pressure column 33. Since, hereby, the cold requirement of the air separation system 110 is already covered beyond requirement, the expansion turbine 46 can be shut off. Depending on the withdrawal rate of the gaseous nitrogen-rich air product (MPGAN), which can be adjusted by a valve which is not shown, a large utilizable amount of a corresponding nitrogen-rich air product (here also designated stream x) is therefore available under pressure, from which energy can be recovered in the expansion turbine 52 and/or the generator thereof. In this case, however, the air must be prewarmed. The use of a corresponding prewarming appliance, however, is complex.

The cold compressor 45 is also in operation in the second operating mode. As likewise explained, with the liquid air products (here LOX and LAIR) more cold is introduced into the cold box of the air separation system 110 than is required, which would lead to the respective temperature profiles in the heat exchangers “shifting” and the temperature of one or more of the streams exiting from the heat exchangers would become colder and colder. From a certain limit, a reliable mode of operation of the air separation system would be no longer ensured. This problem is solved in the air separation system 110 by operating the cold compressor 45 as a heat source. Via the cold compressor 45, however, not only heat may he introduced into the system, but the overall method may be influenced and improved by targeted compression of certain material streams (here stream t), which would not be possible with other heat-producing devices, e.g. air-, steam-, gas- or electrically-heated heat exchangers or heat exchangers heated in other ways. The pressure elevation effected by the cold compressor 43 may be utilized in the expansion turbine 52.

A particular advantage over the air separation system not according to the invention of FIG. 110 results in this case in the air separation system 110 according to the invention which is shown and explained hereinafter, in which the cold compressor 45 is used as what is termed a feed compressor, and is incorporated into the distillation column system 30, in the second operating mode, in other words, at least one gaseous pressurized stream (cf. subsequent streams b to g) is fed to the cold compressor 45 at a temperature level which is below a warm-side temperature of the main heat exchanger 20, is compressed in the cold compressor 45 from a first superatmospheric pressure level to a second superatmospheric pressure: level, and at the second superatmospheric pressure level is fed into at least one distillation column 31, 32 of the distillation column system 30. In other words, in the cold compressor 45, for example, a corresponding gaseous pressurized stream (e.g. air from the main air compressor 10 in the form of she stream e explained hereinafter, or a nitrogen-rich gaseous pressurized stream from one of the distillation columns in the form of the streams b to d, f and g explained hereinafter) is compressed from a pressure level which is used for a low-pressure or medium-pressure column 32 or 33, or generally for a column having a lower pressure than operating pressure, to a pressure level that is used for a medium-pressure or high-pressure column 31 or 32, more generally a column having a higher pressure than operating pressure. After a corresponding cooling in the main heat exchanger 20 (if required), the compressed stream is fed into the corresponding distillation column 31, 32 at a suitable site.

Especially for methods in which, as in the present case, two pressurized streams a and l are provided at different pressure levels by a main compressor 10, this leads to the fact that the rectification is improved. In three-column systems, the fraction of the air that is to be introduced into she high-pressure column 31 and must be compressed to high pressure in advance, becomes less, whereas the fraction of air that is to be introduced into the medium-pressure column and must be compressed to medium pressure in advance becomes higher. The result is that the overall energy consumption of a corresponding air separation system 100 is markedly lower. The cold compressor 45 in this case is advantageously connected in such a manner that the connections (ports) of the expansion engine 46 that is then shut off are used. This reduces the expenditure on apparatus and control technology considerably.

FIG. 3 shows a corresponding air separation system 100 according to an embodiment of the invention in the second operating mode. The first operating mode is not shown again, but corresponds fundamentally to that in FIG. 1: in the first operating mode, a corresponding stream is conducted through the expansion, turbine 46, the cold compressor 45 being bypassed. In the second operating mode that is shown, as in FIG. 2, firstly an oxygen-rich liquid air product. (LOX) is transferred (cf. link B) from the storage tank 61 into the bath evaporator or bath condenser 34 and secondly a liquid air product (for example liquefied air from an external liquefier, here designated LAIR), is fed into the low-pressure column 33 from a further storage tank 63.

The cold compressor 45 is here charged with a substream b of the nitrogen-rich stream y that is taken off from the low-pressure column 33 which is thereby available at the abovementioned superatmospheric pressure level at the top of the low-pressure column 33, for example 1.3 to 1.4 bar. In the cold compressor 45, this substream b is compressed from said (“first”) superatmospheric pressure level to a higher (“second”) superatmospheric pressure level that here corresponds to the operating pressure of the medium-pressure column 32. The substream b compressed as explained is then fed to a passage 25 of the main heat exchanger 20 at an intermediate temperature and is correspondingly cooled. After the cooling, the stream b is applied to the medium-pressure column 32 at the top. Further substreams j (MPGAN) and z (in part used as regeneration gas, REGGAS, optionally only in the first operating mode) can, if necessary, likewise be discharged from the air separation system. The arrangement of the heat exchanger 51 and the expansion turbine 52 is not used.

FIG. 4 shows a further air separation system according to an embodiment of the invention in the second operating mode. The cold compressor 45 is also here charged with a substream of the nitrogen-rich stream y that is taken off from the low-pressure column 33 and is here designated c and is present at the abovementioned superatmospheric pressure level at the top of the low-pressure column 33, for example 1.3 to 1.4 bar. In the cold compressor 45, this substream c is compressed from said (“first”) superatmospheric pressure level to a higher (“second”) superatmospheric pressure level, which here, however, corresponds to the operating pressure of the high-pressure column 31. The substream c that is compressed as explained is then fed to a passage 27 of the main heat exchanger 20 at an intermediate temperature and correspondingly cooled. After the cooling, the stream c is applied to the high-pressure column 31 at the top. Further streams j (MPGAN) and z (used in part as regeneration gas, REGGAS, optionally only in the first operating mode) and also a nitrogen-rich high-pressure stream (HPGAN) can, if required, likewise be passed out of the air separation system.

FIG. 5 shows a further air separation system according to an embodiment of the invention in the second operating mode. The cold compressor 45 is here charged with a stream d which is withdrawn from the medium-pressure column 32 from the top and therefore is available at the above-mentioned superatmospheric pressure level at the top of the medium-pressure column 32 and at the temperature level thereof. In the cold compressor 45 this substream d is compressed from said (“first”) superatmospheric pressure level to a higher (“second”) superatmospheric pressure level that here corresponds again to the operating pressure of the high-pressure column 31. The substream d that is compressed as explained is then fed to a corresponding passage 27 of the main heat exchanger 20 at an intermediate temperature and correspondingly cooled. After the cooling, the stream d is applied to the high-pressure column 31 at the top. Further streams j (MPGAN) and z (used in part as regeneration gas, REGGAS, optionally only in the first operating mode), and also a nitrogen-rich high-pressure stream (HPGAN) can likewise be passed out as required from the air separation system.

FIG. 6 shows a further air separation system according to an embodiment of the invention in the second operating mode. The cold compressor 45 is here charged with a substream e of the pressurized stream l from the main air compressor 10 which is present at the above-mentioned superatmospheric pressure level that corresponds to the operating pressure of the medium-pressure column 32. The substream e is taken off from the main heat exchanger 20 at the cold end, in such a manner that the temperature level thereof is below the warm-side temperature level of the main heat exchanger 20. In the cold compressor 45, this substream e is compressed from said (“first”) superatmospheric pressure level to a higher (“second”) superatmospheric pressure level that in turn here corresponds to the operating pressure of the high-pressure column 31. The substream e that is compressed as explained is then fed to the passage 21 of the main heat exchanger 20 at an intermediate temperature, and thereby combined with the stream a. The stream which is here further designated a is correspondingly cooled. After the cooling, the stream a is fed into the high-pressure column 31. Further streams i (MPGAN) and z (used in part as regeneration gas, REGGAS, optionally only in the first operating mode) can, as above, likewise be passed out as required from the air separation system.

FIG. 7 shows a further air separation system, according to an embodiment of the invention in the second operating mode. The cold compressor 45 is here charged with a stream f which is withdrawn from the low-pressure column 33 and is therefore present at the above-mentioned superatmospheric pressure level of the low-pressure column 33, for example 1.3 to 1.4 bar, and is present at the temperature level thereof. In the cold compressor 15, this substream f is compressed from said (“first”) superatmospheric pressure level to a higher (“second”) superatmospheric pressure level that here corresponds in turn to the operating pressure of the medium-pressure column 32. The substream f that is compressed as explained is then fed to the passage 24 of the main heat exchanger 20 at an intermediate temperature and is thereby combined with the stream l. The stream here further designated l is correspondingly cooled. After cooling, the stream l is fed into the medium-pressure column 32. Further streams l (MEGAN) and z (in part used as regeneration gas, REGGAS, optionally only in the first operating mode) can, as above, be likewise passed out or the air separation, system as required.

FIG. 8 shows a further air separation system according to an embodiment of the invention in the second operating mode. The cold, compressor 45 is here also charged with a stream g which is withdrawn from the low-pressure column 33 and is therefore present at the abovementioned superatmospheric pressure level of the low-pressure column 33, for example 1.3 to 1.4 bar, and at the temperature level thereof. In the cold compressor 45, this substream g is compressed from said (“first”) superatmospheric pressure level to a higher (“second”) superatmospheric pressure level that here in turn corresponds to the operating pressure of the high-pressure column 31, for example 5.0 to 5.5 bar. The substream g that is compressed as explained is then fed to the passage 21 of the main heat exchanger 20 at an intermediate temperature and thereby combined, with the stream a. The stream which is further here designated a is correspondingly cooled. After the cooling, the stream a is inter alia fed into the high-pressure column 31. Further streams j (MPGAN) and z (in part used as regeneration gas, REGGAS, optionally only in the first operating mode) can likewise be passed out of the air separation system as required.

FIGS. 9 and 10 show alternative possibilities for arranging a cold compressor 45 in a schematic partial representation. The corresponding streams are not provided again with reference signs. These possibilities can be achieved in all systems which are shown in FIGS. 3 to 8 and in further embodiments of the invention that are not shown.

In accordance with FIG. 9, a stream that is compressed by the cold compressor 45 is fed on the warm, side to the main heat exchanger 20. In accordance with FIG. 10, a stream is withdrawn from the main heat exchanger 20 at a first intermediate temperature, then compressed, and fed again to the main heat exchanger 20 at a second intermediate temperature. 

1. A method for producing at least one air product, in which an air separation system that has a main air compressor, a main heat exchanger and a distillation column system that comprises a high-pressure column, a medium-pressure column, a low-pressure column, a low-pressure column-sump evaporator and a low-pressure column intermediate evaporator, wherein the high-pressure column is operated at a higher operating pressure than the low-pressure column, the medium-pressure column is operated at an operating pressure which is between the operating pressures of the high-pressure column and the low-pressure column, and the low-pressure column sump evaporator and the low-pressure column intermediate evaporator are constructed as condenser-evaporators, characterized in that the method comprises a first and second operating mode, wherein in the first operating mode, at least one liquid air product produced in the distillation column system is stored and in the second operating mode the at least one liquid air product that is stored in the first mode of operation and/or at least one further liquid air product is fed into the distillation column system and at least one gaseous pressurized stream that is at a temperature level that is below a warm-side temperature of the main heat exchanger is fed to a cold compressor, is compressed in the cold compressor from a first superatmospheric pressure level to a second superatmospheric pressure level, and at the second pressure level is at least in part fed into at least one distillation column of the distillation column system.
 2. The method as claimed in claim 1, in which, in the first operating mode, the at least one pressurized stream, and/or at least one further gaseous pressurized stream is cold-producingly expanded in an expansion turbine.
 3. The method as claimed in claim 1, in which oxygen-enriched stream from the sump of the low-pressure column is vaporized in a side condenser to provide a gaseous oxygen pressurized product, wherein the side condenser is constructed as a condenser-evaporator.
 4. The method as claimed in claim 1, in which the first pressure level corresponds to the operating pressure of the low-pressure column and/or the second pressure level corresponds to the operating pressure of the high-pressure column.
 5. The method as claimed in claim 1, in which the first pressure level corresponds to the operating pressure of the low-pressure column, and the second pressure level corresponds to the operating pressure of the medium-pressure column or the high-pressure column, or in which the first pressure level corresponds to the operating pressure of the medium-pressure column, and the second pressure level corresponds to the operating pressure of the high-pressure column.
 6. The method as claimed in claim 1, in which the at least one gaseous pressurized stream is formed from at least a part of a stream that is withdrawn from a distillation column of the distillation column system, which distillation column is operated at the first pressure level as operating pressure.
 7. The method as claimed in claim 1, in which the at least one gaseous pressurized stream is formed from at least a part of a stream that is provided by means of the main air compressor and is cooled by means of the main heat exchanger.
 8. The method as claimed in claim 1, in which the at least one gaseous pressurized stream, before it is fed into the at least one distillation column of the distillation column system, is combined at the second pressure level with at least one further stream.
 9. The method as claimed in claim 1, which the at least one gaseous pressurized stream, after the compression in the cold compressor, is at least in part cooled in the main heat exchanger.
 10. The method as claimed in claim 9, in which the at least one gaseous pressurized stream, after the compression in the cold compressor, is fed for cooling to the main heat exchanger on the warm side, or at a further temperature level which is below a warm-side temperature of the main heat exchanger.
 11. The method as claimed in claim 1, in which a part of the gaseous pressurized stream compressed in the cold compressor is warmed in the main heat exchanger and/or is discharged at least in part from the air separation system.
 12. An air separation system that comprises a main air compressor, a main heat exchanger, and a distillation column system and is equipped for operation in first and second operating modes, wherein means are provided which are equipped to store, in the first operating mode, at least one liquid air product produced in the distillation column system, and, in the second operating mode to feed at least one liquid air product that is stored in the first operating mode and/or at least one further liquid air product into the distillation column system, characterized in that the air separation plant comprises a cold compressor, and in that means are provided which are suitable to feed, in the second operating mode, at least one gaseous pressurized stream at a temperature level that is below a warm-side temperature of the main heat exchanger to the cold compressor, to compress it in the cold compressor from a first superatmospheric pressure level to a second superatmospheric pressure level, and then to feed it at the second pressure level at least in part into at least one distillation column of the distillation column system.
 13. A method for producing electrical energy, in which at least one air product is produced, in which an air separation,system that has a main air compressor, a main heat exchanger and a distillation column system that comprises a high-pressure column, a medium-pressure column, a low-pressure column, a low-pressure column-sump evaporator and a low-pressure column Intermediate evaporator, wherein the high-pressure column is operated at a higher operating pressure than the low-pressure column, the medium-press column is operated at an operating pressure which is between the operating pressures of the high-pressure column and the low-pressure column, and the low-pressure column sump evaporator and the low pressure column intermediate evaporator are constructed as condenser-evaporators, characterized in that the method comprises a first and second operating mode, wherein in the first operating mode, at least one liquid air product produced in the distillation column system is stored and in the second operating mode the at least one liquid air product that is stored in the first mode of operation and/or at least one further liquid air product is fed into the distillation column system and at least one gaseous pressurized stream that is at a temperature level that is below a warm-side temperature of the main heat exchanger is fed to a cold compressor, is compressed in the cold compressor from a first superatmospheric pressure level to a second superatmospheric pressure level, and at the second pressure level is at least in part fed into at least one distillation column of the distillation column system at least during the second operating mode, and is used for producing and/or reacting at least one fuel.
 14. The method as claimed in claim 13, further comprising an oxyfuel method and/or a combined process with integrated gasification. 